<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <div id="app">
    <h2>{{count}}</h2>
    <button v-on:click="add">+</button>
    <button @click="jian">-</button>
  </div>
  <script src="../js/vue.js"></script>
  <script>
    var app = new Vue({
      el: '#app',
      data: {
        count: 0
      },
      methods: {
        add() {
          this.count++
        },
        jian() {
          this.count--
        }
      }
    });
  </script>

</body>

</html>